Steroid hormones are important chemical carriers of information serving for the long-term and global control of cellular functions. They control the growth and the differentiation and function of many organs. On the other hand, they may also have negative effects and favor the pathogenesis and proliferation of diseases in the organism, such as mammary and prostate cancers (Deroo, B. J. et al., J. Clin. Invest., 116: 561-570 (2006); Fernandez, S. V. et al., Int. J. Cancer, 118: 1862-1868 (2006)).
The biosynthesis of steroids takes place in the testes or ovaries, where sex hormones are produced. In addition, the production of glucocorticoids and mineral corticoids takes place in the adrenal glands. Moreover, individual synthetic steps also occur outside the glands, namely in the brain or in the peripheral tissue, e.g., adipose tissue (Bulun, S. E. et al., J. Steroid Biochem. Mol. Biol., 79: 19-25 (2001); Gangloff, A. et al., Biochem. J., 356: 269-276 (2001)). In this context, Labrie coined the term “intracrinology” in 1988 (Labrie, C. et al., Endocrinology, 123: 1412-1417 (1988); Labrie, F. et al., Ann. Endocrinol. (Paris), 56: 23-29 (1995); Labrie, F. et al., Horm. Res., 54: 218-229 (2000)). Attention was thus focused on the synthesis of steroids that are formed locally in peripheral tissues and also display their action there without getting into the blood circulation. The intensity of the activity of the hormones is modulated in the target tissue by means of various enzymes.
Thus, it could be shown that the 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1), which catalyzes the conversion of estrone to estradiol, is more abundant in endometriotic tissue and breast cancer cells while there is a deficiency in 17β-HSD type 2, which catalyzes the reverse reaction (Bulun, S. E. et al., J. Steroid Biochem. Mol. Biol., 79: 19-25 (2001); Miyoshi, Y. et al., Int. J. Cancer, 94: 685-689 (2001)).
A major class of steroid hormones is formed by the estrogens, the female sex hormones, whose biosynthesis takes place mainly in the ovaries and reaches its maximum immediately before ovulation. However, estrogens also occur in the adipose tissue, muscles and some tumors. Their main functions include a genital activity, i.e., the development and maintenance of the female sexual characteristics as well as an extragenital lipid-anabolic activity leading to the development of subcutaneous adipose tissue. In addition, they are involved in the pathogenesis and proliferation of estrogen-related diseases, such as endometriosis, endometrial carcinoma, adenomyosis and breast cancer (Bulun, S. E. et al., J. Steroid Biochem. Mol. Biol., 79: 19-25 (2001); Miyoshi, Y. et al., Int. J. Cancer, 94: 685-689 (2001); Gunnarsson, C. et al., Cancer Res., 61: 8448-8451 (2001); Kitawaki, J., Journal of Steroid Biochemistry & Molecular Biology, 83: 149-155 (2003); Vihko, P. et al., J. Steroid. Biochem. Mol. Biol., 83: 119-122 (2002); Vihko, P. et al., Mol. Cell. Endocrinol., 215: 83-88 (2004)).
The most potent estrogen is estradiol (E2), which is formed in premenopausal females, mainly in the ovaries. On an endocrine route, it arrives at the target tissues, where it displays its action by means of an interaction with the estrogen receptor (ER) α. After the menopause, the plasma E2 level decreases to 1/10 of the estradiol level found in premenopausal females (Santner, S. J. et al., J. Clin. Endocrinol. Metab., 59: 29-33 (1984)). E2 is mainly produced in the peripheral tissue, e.g., breast tissue, endometrium, adipose tissue and skin, from inactive precursors, such as estrone sulfate (E1-S), dehydroepiandrosterone (DHEA) and DHEA-S. These reactions occur with the participation of various steroidogenic enzymes (hydroxysteroid dehydrogenases, aromatase), which are in part more abundantly produced in the peripheral tissue, where these active estrogens display their action. As a consequence of such intracrine mechanism for the formation of E2, its concentration in the peripheral tissue, especially in estrogen-related diseases, is higher than that in the healthy tissue. Above all, the growth of many breast cancer cell lines is stimulated by a locally increased estradiol concentration. Further, the occurrence and progress of diseases such as endometriosis, leiomyosis, adenomyosis, menorrhagia, metrorrhagia and dysmenorrhea is dependent on a significantly increased estradiol level in accordingly diseased tissue.
Endometriosis is an estrogen-related disease afflicting about 5 to 10% of all females of childbearing age (Kitawaki, J., Journal of Steroid Biochemistry & Molecular Biology, 83: 149-155 (2003)). From 35 to 50% of the females suffering from abdominal pain and/or sterility show signs of endometriosis (Urdl, W., J. Reproduktionsmed. Endokrinol., 3: 24-30 (2006)). This diseases is defined as a histologically detected ectopic endometrial glandular and stromal tissue. In correspondingly severe cases, this chronic disease, which tends to relapse, leads to pain of different intensities and variable character and possibly to sterility. Three macroscopic clinical pictures are distinguished: peritoneal endometriosis, retroperitoneal deep-infiltrating endometriosis including adenomyosis uteri, and cystic ovarial endometriosis. There are various explanatory theories for the pathogenesis of endometriosis, e.g., the metaplasia theory, the transplantation theory and the theory of autotraumatization of the uterus as established by Leyendecker (Leyendecker, G. et al., Hum. Reprod., 17: 2725-2736 (2002)).
According to the metaplasia theory (Meyer, R., Zentralbl. Gynäkol., 43: 745-750 (1919); Nap, A. W. et al., Best Pract. Res. Clin. Obstet. Gynaecol., 18: 233-244 (2004)), pluripotent coelomic epithelium is supposed to have the ability to differentiate and form endometriotic foci even in adults under certain conditions. This theory is supported by the observation that endometrioses, in part severe ones, can occur in females with lacking uterus and gynastresy. Even in males who were treated with high estrogen doses due to a prostate carcinoma, an endometriosis could be detected in singular cases.
According to the theory postulated by Sampson (Halme, J. et al., Obstet. Gynecol., 64: 151-154 (1984); Sampson, J., Boston Med. Surg. J., 186: 445-473 (1922); Sampson, J., Am. J. Obstet. Gynecol., 14: 422-469 (1927)), retrograde menstruation results in the discharge of normal endometrial cells or fragments of the eutopic endometrium into the abdominal cavity with potential implantation of such cells in the peritoneal space and further development to form endometriotic foci. Retrograde menstruation could be detected as a physiological event. However, not all females with retrograde menstruation become ill with endometriosis, but various factors, such as cytokines, enzymes, growth factors (e.g., matrix metalloproteinases), play a critical role.
The enhanced autonomous non-cyclical estrogen production and activity as well as the reduced estrogen inactivation are typical peculiarities of endometriotic tissue. This enhanced local estrogen production and activity is caused by a significant overexpression of aromatase, expression of 17β-HSD1 and reduced inactivation of potent E2 due to a lack of 17β-HSD2, as compared to the normal endometrium (Bulun, S. E. et al., J. Steroid Biochem. Mol. Biol., 79: 19-25 (2001); Kitawaki, J., Journal of Steroid Biochemistry & Molecular Biology, 83: 149-155 (2003); Karaer, O. et al., Acta. Obstet. Gynecol. Scand., 83: 699-706 (2004); Zeitoun, K. et al., J. Clin. Endocrinol. Metab., 83: 4474-4480 (1998)).
The polymorphic symptoms caused by endometriosis include any pain symptoms in the minor pelvis, back pain, dyspareunia, dysuria and defecation complaints.
One of the therapeutic measures employed most frequently in endometriosis is the surgical removal of the endometriotic foci (Urdl, W., J. Reproduktionsmed. Endokrinol., 3: 24-30 (2006)). Despite new therapeutic concepts, medicamental treatment remains in need of improvement. The purely symptomatic treatment of dysmenorrhea is effected by means of non-steroidal anti-inflammatory drugs (NSAID), such as acetylsalicylic acid, indomethacine, ibuprofen and diclofenac. Since a COX2 overexpression could be observed both in malignant tumors and in the eutopic endometrium of females with endometriosis, a therapy with the selective COX2 inhibitors, such as celecoxib, suggests itself (Fagotti, A. et al., Hum. Reprod. 19: 393-397 (2004); Hayes, E. C. et al., Obstet. Gynecol. Surv., 57: 768-780 (2002)). Although they have a better gastro-intestinal side effect profile as compared to the NSAID, the risk of cardiovascular diseases, infarction and stroke is increases, especially for patients with a predamaged cardiovascular system (Dogne, J. M. et al., Curr. Pharm. Des., 12: 971-975 (2006)). The causal medicamental theory is based on estrogen deprivation with related variable side effects and a generally contraceptive character. The gestagens with their anti-estrogenic and antiproliferative effect on the endometrium have great therapeutic significance. The most frequently employed substances include medroxyprogesterone acetate, norethisterone, cyproterone acetate. The use of danazole is declining due to its androgenic side effect profile with potential gain of weight, hirsutism and acne. The treatment with GnRH analogues is of key importance in the treatment of endometriosis (Rice, V.; Ann. NY Acad. Sci., 955: 343-359 (2001)); however, the duration of the therapy should not exceed a period of 6 months since a longer term application is associated with irreversible damage and an increased risk of fracture. The side effect profile of the GnRH analogues includes hot flushes, amenorrhea, loss of libido and osteoporosis, the latter mainly within the scope of a long term treatment.
Another therapeutic approach involves the steroidal and non-steroidal aromatase inhibitors. It could be shown that the use of the non-steroidal aromatase inhibitor letrozole leads to a significant reduction of the frequency and severity of dysmenorrhea and dyspareunia and to a reduction of the endometriosis marker CA125 level (Soysal, S. et al., Hum. Reprod., 19: 160-167 (2004)). The side effect profile of aromatase inhibitors ranges from hot flushes, nausea, fatigue to osteoporosis and cardiac diseases. Long term effects cannot be excluded.
All the possible therapies mentioned herein are also employed in the combatting of diseases such as leiomyosis, adenomyosis, menorrhagia, metrorrhagia and dysmenorrhea.
Every fourth cancer disease in the female population falls under the category of mammary cancers. This disease is the main cause of death in the Western female population at the age of from 35 to 54 years (Nicholls, P. J., Pharm. J., 259: 459-470 (1997)). Many of these tumors exhibit an estrogen-dependent growth and are referred to as so-called HDBC (hormone dependent breast cancer). A distinction is made between ER+ and ER− tumors. The classification criteria are important to the choice of a suitable therapy. About 50% of the breast cancer cases in premenopausal females and 75% of the breast cancer cases in postmenopausal females are ER+ (Coulson, C., Steroid biosynthesis and action, 2nd edition, 95-122 (1994); Lower, E. et al., Breast Cancer Res. Treat., 58: 205-211 (1999)), i.e., the growth of the tumor is promoted by as low as physiological concentrations of estrogens in the diseased tissue.
The therapy of choice at an early stage of breast cancer is surgical measures, if possible, breast-preserving surgery. Only in a minor number of cases, mastectomy is performed. In order to avoid relapses, the surgery is followed by radiotherapy, or else radiotherapy is performed first in order to reduce a larger tumor to an operable size. In an advanced state, or when metastases occur in the lymph nodes, skin or brain, the objective is no longer to heal the disease, but to achieve a palliative control thereof.
The therapy of the mammary carcinoma is dependent on the hormone receptor status of the tumor, on the patient's hormone status and on the status of the tumor (Paepke, S. et al., Onkologie, 26 Suppl., 7: 4-10 (2003)). Various therapeutical approaches are available, but all are based on hormone deprivation (deprivation of growth-promoting endogenous hormones) or hormone interference (supply of exogenous hormones). However, a precondition of such responsiveness is the endocrine sensitivity of the tumors, which exists with HDBC ER+ tumors. The drugs employed in endocrine therapy include GnRH analogues, anti-estrogens and aromatase inhibitors. GnRH analogues, such as gosereline, will bind to specific membrane receptors in the target organ, the pituitary gland, which results in an increased secretion of FSH and LH. These two hormones in turn lead to a reduction of GnRH receptors in a negative feedback loop in the pituitary cells. The resulting desensitization of the pituitary cells towards GnRH leads to an inhibition of FSH and LH secretion, so that the steroid hormone feedback loop is interrupted. The side effects of such therapeutic agents include hot flushes, sweats and osteoporosis.
Another therapeutic option is the use of anti-estrogens, antagonists at the estrogen receptor. Their activity is based on the ability to competitively bind to the ER and thus avoid the specific binding of the endogenous estrogen. Thus, the natural hormone is no longer able to promote tumor growth. Today, therapeutic use involves so-called SERM (selective estrogen receptor modulators), which develop estrogen agonism in tissues such as bones or liver, but have antagonistic and/or minimal agonistic effects in breast tissue or uterus (Holzgrabe, U., Pharm. Unserer Zeit, 33: 357-359 (2004); Pasqualini, J. R., Biochim. Biophys. Acta., 1654: 123-143 (2004); Sexton, M. J. et al., Prim Care Update Ob Gyns, 8: 25-30 (2001)). Thus, these compounds are not only effective in combatting breast cancer, but also increase the bone density and reduce the risk of osteoporosis in postmenopausal females. The use of the SERM tamoxifen is most widely spread. However, after about 12-18 months of treatment, there is development of resistance, an increased risk of endometrial cancers and thrombo-embolic diseases due to the partial agonistic activity at the ER (Goss, P. E. et al., Clin. Cancer Res., 10: 5717-5723 (2004); Nunez, N. P. et al., Clin. Cancer Res., 10: 5375-5380 (2004)).
The enzymatically catalyzed estrogen biosynthesis may also be influenced by selective enzyme inhibitors. The enzyme aromatase, which converts C19 steroids to C18 steroids, was one of the first targets for lowering the estradiol level. This enzyme complex, which belongs to the cytochrome P-450 enzymes, catalyzes the aromatization of the androgenic A ring to form estrogens. The methyl group at position 10 of the steroid is thereby cleaved off. The first aromatase inhibitor employed for the therapy of breast cancer was aminogluthetimide. However, aminogluthetimide affects several enzymes of the cytochrome P-450 superfamily and thus inhibits a number of other biochemical conversions. For example, among others, the compound interferes with the steroid production of the adrenal glands so heavily that a substitution of both glucocorticoids and mineral corticoids may be necessary. In the meantime, more potent and more selective aromatase inhibitors, which can be subdivided into steroidal and non-steroidal compounds, are on the market. The steroidal inhibitors include, for example, exemestane, which has a positive effect on the bone density, which is associated with its affinity for the androgen receptor (Goss, P. E. et al., Clin. Cancer Res., 10: 5717-5723 (2004)). However, this type of compounds are irreversible inhibitors that also have a substantial number of side effects, such as hot flushes, nausea, fatigue. However, there are also non-steroidal compounds that are employed therapeutically, for example, letrozole. The advantage of these compounds resides in the lesser side effects, they do not cause uterine hypertrophy, but have no positive effect on the bone density and result in an increase of LDL (low density lipoprotein), cholesterol and triglyceride levels (Goss, P. E. et al., Clin. Cancer Res., 10: 5717-5723 (2004); Nunez, N. P. et al., Clin. Cancer Res., 10: 5375-5380 (2004)). Today, aromatase inhibitors are predominantly employed as second-line therapeutic agents. In the meantime, however, the equivalence or even superiority of aromatase inhibitors to SERM, such as tamoxifene, has been proven in clinical studies (Geisler, J. et al., Crit. Rev. Oncol. Hematol., 57: 53-61 (2006); Howell, A. et al., Lancet, 365: 60-62 (2005)). Thus, the use of aromatase inhibitors also as first-line therapeutical agents is substantiated.
However, the estrogen biosynthesis in the peripheral tissue also includes other pathways for the production of E1 and the more potent E2 by avoiding the enzyme aromatase that is locally present in the target tissue, for example, breast tumors. Two pathways for the production of estrogens in breast cancer tissue are postulated (Pasqualini, J. R., Biochim. Biophys. Acta., 1654: 123-143 (2004)), the aromatase pathway (Abul-Hajj, Y. J. et al., Steroids, 33: 205-222 (1979); Lipton, A. et al., Cancer, 59: 779-782 (1987)) and the sulfatase pathway (Perel, E. et al., J. Steroid. Biochem., 29: 393-399 (1988)). The aromatase pathway includes the production of estrogens from androgens with participation of the enzyme aromatase. The sulfatase pathway is the pathway for the production of estrone/estradiol by means of the enzyme steroid sulfatase, an enzyme that catalyzes the conversion of estrone sulfate and DHEA-S to estrone and DHEA. In this way, 10 times as much estrone is formed in the target tissue as compared to the aromatase pathway (Santner, S. J. et al., J. Clin. Endocrinol. Metab., 59: 29-33 (1984)). The estrone is then reduced by means of the enzyme 17β-HSD1 to form E2, the most potent estrogen. Steroid sulfatase and 17β-HSD1 are new targets in the battle against estrogen-related diseases, especially for the development of therapeutic agents for mammary carcinomas (Pasqualini, J. R., Biochim. Biophys. Acta., 1654: 123-143 (2004)).
Numerous steroidal sulfatase inhibitors could be found, including the potent irreversible inhibitor EMATE, which exhibited an agonistic activity at the estrogen receptor, however (Ciobanu, L. C. et al., Cancer Res., 63: 6442-6446 (2003); Hanson, S. R. et al., Angew. Chem. Int. Ed. Engl., 43: 5736-5763 (2004)). Some potent non-steroidal sulfatase inhibitors could also be found, such as COUMATE and derivatives as well as numerous sulfamate derivatives of tetrahydronaphthalene, indanone and tetralone (Hanson, S. R. et al., Angew. Chem. Int. Ed. Engl., 43: 5736-5763 (2004)). However, no sulfatase inhibitor has been able to enter the therapy of estrogen-related diseases to date.
The inhibition of 17β-HSD1, a key enzyme in the biosynthesis of E2, the most potent estrogen, could suggest itself as an option in the therapy of estrogen-related diseases in both premenopausal and postmenopausal females (Kitawaki, J., Journal of Steroid Biochemistry & Molecular Biology, 83: 149-155 (2003); Allan, G. M. et al., Mol. Cell. Endocrinol., 248: 204-207 (2006); Penning, T. M., Endocr. Rev., 18: 281-305 (1997); Sawicki, M. W. et al., Proc. Natl. Acad. Sci. USA, 96: 840-845 (1999); Vihko, P. et al., Mol. Cell. Endocrinol., 171: 71-76 (2001)). An advantage of this approach is the fact that the intervention is effected in the last step of estrogen biosynthesis, i.e., the conversion of E1 to the highly potent E2 is inhibited. The intervention is effected in the biosynthetic step occurring in the peripheral tissue, so that a reduction of estradiol production takes place locally in the diseased tissue. The use of correspondingly selective inhibitors would probably be associated with little side effects since the synthesis of other steroids would remain unaffected. It would be important that such inhibitors exhibit no or only very little agonistic activity at the ER, especially at the ER α, since agonistic binding is accompanied by an activation and thus proliferation and differentiation of the target cell. In contrast, an antagonistic activity of such compounds at the ER would prevent the natural substrates from binding at the receptor and result in a further reduction of the proliferation of the target cells. The use of selective 17β-HSD1 inhibitors for the therapy of numerous estrogen-dependent diseases is discussed, for example, for breast cancer, tumors of the ovaries, prostate carcinoma, endometrial carcinoma, endometriosis, adenomyosis. Highly interesting and completely novel is the proposal to employ selective inhibitors of 17β-HSD1 for prevention when there is a genetic disposition for breast cancer (Miettinen, M. et al., J. Mammary Gland. Biol. Neoplasia, 5: 259-270 (2000)).
Hydroxysteroid dehydrogenases (HSD) can be subdivided into different classes. The 11β-HSD modulate the activity of glucocorticoids, 3β-HSD catalyzes the reaction of Δ5-3β-hydroxysteroids (DHEA or 5-androstene-3β,17β-diol) to form Δ5-3β-ketosteroids (androstenedione or testosterone). 17β-HSD convert the less active 17-ketosteroids to the corresponding highly active 17-hydroxy compounds (androstenedione to testosterone and E1 to E2) or conversely (Payne, A. H. et al., Endocr. Rev., 25: 947-970 (2004); Peltoketo, H. et al., J. Mol. Endocrinol., 23: 1-11 (1999); Suzuki, T. et al., Endocr. Relat. Cancer, 12: 701-720 (2005)). Thus, the HSD play a critical role in both the activation and the inactivation of steroid hormones. Depending on the cell's need for steroid hormones, they alter the potency of the sex hormones (Penning, T. M., Endocr. Rev., 18: 281-305 (1997)), for example, E1 is converted to the highly potent E2 by means of 17β-HSD1, while E2 is converted to the less potent E1 by means of 17β-HSD2; 17β-HSD2 inactivates E2 while 17β-HSD1 activates E1.
To date, fourteen different 17β-HSDs have been identified (Mindnich, R. et al., Mol. Cell. Endocrinol., 218: 7-20 (2004); Lukacik, P. et al., Mol. Cell. Endocrinol., 248: 61-71 (2006)), and twelve of these enzymes could be cloned (Suzuki, T. et al., Endocr. Relat. Cancer, 12: 701-720 (2005)). They all belong to the so-called short chain dehydrogenase/reductase (SDR) family, with the exception of 17β-HSD5, which is a ketoreductase. The amino acid identity between the different 17β-HSDs is as low as 20-30% (Luu-The, V., J. Steroid Biochem. Mol. Biol., 76: 143-151 (2001)), and they are membrane-bound or soluble enzymes. The X-ray structure of 6 human subtypes is known (1,4,5,10,11,14) (Ghosh, D. et al., Structure, 3: 503-513 (1995); Kissinger, C. R. et al., J. Mol. Biol., 342: 943-952 (2004); Zhou, M. et al., Acta Crystallogr. D. Biol. Crystallogr., 58: 1048-1050 (2002). The 17β-HSDs are NAD(H)-dependent and NADP(H)-dependent enzymes. They play a critical role in the hormonal regulation in humans. The enzymes are distinguished by their tissue distribution, catalytic preference (oxidation or reduction), substrate specificity and subcellular localization. The same HSD subtype was found in different tissues. It is likely that all 17β-HSDs are expressed in the different estrogen-dependent tissues, but in different concentrations. In diseased tissue, the ratio between the different subtypes is altered as compared to healthy tissue, some subtypes being overexpressed while others may be absent. This may cause an increase or decrease of the concentration of the corresponding steroid. Thus, the 17β-HSDs play an extremely important role in the regulation of the activity of the sex hormones. Further, they are involved in the development of estrogen-sensitive diseases, such as breast cancer, ovarian, uterine and endometrial carcinomas, as well as androgen-related diseases, such as prostate carcinoma, benign prostate hyperplasia, acne, hirsutism etc. It has been shown that some 17β-HSDs are also involved in the development of further diseases, e.g., pseudohermaphrodism (17β-HSD3 (Geissler, W. M. et al., Nat. Genet., 7: 34-39 (1994))), bifunctional enzyme deficiency (17β-HSD4 (van Grunsven, E. G. et al., Proc. Natl. Acad. Sci. USA, 95: 2128-2133 (1998))), polycystic kidney diseases (17β-HSD8 (Maxwell, M. M. et al., J. Biol. Chem., 270: 25213-25219 (1995))) and Alzheimer's (17β-HSD10 (Kissinger, C. R. et al., J. Mol. Biol., 342: 943-952 (2004); He, X. Y. et al., J. Biol. Chem., 274: 15014-15019 (1999); He, X. Y. et al., Mol. Cell. Endocrinol., 229: 111-117 (2005); He, X. Y. et al., J. Steroid Biochem. Mol. Biol., 87: 191-198 (2003); Yan, S. D. et al., Nature, 389: 689-695 (1997))).
The best characterized member of the 17β-HSDs is the type 1 17β-HSD. The 17β-HSD1 is an enzyme from the SDR family, also referred to as human placenta estradiol dehydrogenase (Gangloff, A. et al., Biochem. J., 356: 269-276 (2001); Jornvall, H. et al., Biochemistry, 34: 6003-6013 (1995)). Its designation as assigned by the enzyme commission is E.C.1.1.1.62.
Engel et al. (Langer, L. J. et al., J. Biol. Chem., 233: 583-588 (1958)) were the first to describe this enzyme in the 1950's. In the 1990's, first crystallization attempts were made, so that a total of 16 crystallographic structures can be recurred to today in the development of inhibitors (Alho-Richmond, S. et al., Mol. Cell. Endocrinol., 248: 208-213 (2006)). Available are X-ray structures of the enzyme alone, but also of binary and ternary complexes of the enzyme with its substrate and other ligands or substrate/ligand and cofactor.
17β-HSD1 is a soluble cytosolic enzyme. NADPH serves as a cofactor. 17β-HSD1 is encoded by a 3.2 kb gene consisting of 6 exons and 5 introns that is converted to a 2.2 kb transcript (Luu-The, V., J. Steroid Biochem. Mol. Biol., 76: 143-151 (2001); Labrie, F. et al., J. Mol. Endocrinol., 25: 1-16 (2000)). It is constituted by 327 amino acids. The molecular weight of the monomer is 34.9 kDa (Penning, T. M., Endocr. Rev., 18: 281-305 (1997)). 17β-HSD1 is expressed in the placenta, liver, ovaries, endometrium, prostate gland, peripheral tissue, such as adipose tissue and breast cancer cells (Penning, T. M., Endocr. Rev., 18: 281-305 (1997)). It was isolated for the first time from human placenta (Jarabak, J. et al., J. Biol. Chem., 237: 345-357 (1962)). The main function of 17β-HSD1 is the conversion of the less active estrone to the highly potent estradiol. However, it also catalyzes to a lesser extent the reaction of dehydroepiandrosterone (DHEA) to 5-androstene-3β,17β-diol, an androgen showing estrogenic activity (Labrie, F., Mol. Cell. Endocrinol., 78: C113-118 (1991); Poirier, D., Curr. Med. Chem., 10: 453-477 (2003); Poulin, R. et al., Cancer Res., 46: 4933-4937 (1986)). In vitro, the enzyme catalyzes the reduction and oxidation between E1 and E2 while it catalyzes only the reduction under physiological conditions. These bisubstrate reactions proceed according to a random catalytic mechanism, i.e., either the steroid or the cofactor is first to bind to the enzyme (Betz, G., J. Biol. Chem., 246: 2063-2068 (1971)). A catalytic mechanism in which the cofactor binds to the enzyme first is also postulated (Neugebauer, A. et al., Bioorg. Med. Chem., eingereicht (2005)).
The enzyme consists of a substrate binding site and a channel that opens into the cofactor binding site. The substrate binding site is a hydrophobic tunnel having a high complementarity to the steroid. The 3-hydroxy and 17-hydroxy groups in the steroid form four hydrogen bonds to the amino acid residues His221, Glu282, Ser142 and Tyr155. The hydrophobic van der Waals interactions seem to form the main interactions with the steroid while the hydrogen bonds are responsible for the specificity of the steroid for the enzyme (Labrie, F. et al., Steroids, 62: 148-158 (1997)). Like with all the other enzymes of this family, what is present as a cofactor binding site is the Rossmann fold, which is a region consisting of α-helices and β-sheets (β-α-β-α-β)2, a generally occurring motif Gly-Xaa-Xaa-Xaa-Gly-Xaa-Gly, and a nonsense region Tyr-Xaa-Xaa-Xaa-Lys within the active site. What is important to the activity is a catalytic tetrade consisting of Tyr155-Lys159-Ser142-Asn114, which stabilize the steroid and the ribose in the nicotinamide during the hydride transfer (Alho-Richmond, S. et al., Mol. Cell. Endocrinol., 248: 208-213 (2006); Labrie, F. et al., Steroids, 62: 148-158 (1997); Nahoum, V. et al., Faseb. J., 17: 1334-1336 (2003)).
The gene encoding 17β-HSD1 is linked with the gene for mammary and ovarian carcinomas that is very susceptible to mutations and can be inherited, the BRCA1 gene, on chromosome 17q11-q21 (Labrie, F. et al., J. Mol. Endocrinol., 25: 1-16 (2000)). As has been demonstrated, the activity of 17β-HSD1 is higher in endometrial tissue and breast cancer cells as compared to healthy tissue, which entails high intracellular estradiol levels, which in turn cause proliferation and differentiation of the diseased tissue (Bulun, S. E. et al., J. Steroid Biochem. Mol. Biol., 79: 19-25 (2001); Miyoshi, Y. et al., Int. J. Cancer, 94: 685-689 (2001); Kitawaki, J., Journal of Steroid Biochemistry & Molecular Biology, 83: 149-155 (2003); Pasqualini, J. R., Biochim. Biophys. Acta., 1654: 123-143 (2004); Vihko, P. et al., Mol. Cell. Endocrinol., 171: 71-76 (2001); Miettinen, M. et al., Breast Cancer Res. Treat., 57: 175-182 (1999); Sasano, H. et al., J. Clin. Endocrinol. Metab., 81: 4042-4046 (1996); Yoshimura, N. et al., Breast Cancer Res., 6: R46-55 (2004)). An inhibition of 17β-HSD1 could result in the estradiol level being lowered and thus lead to a regression of the estrogen-related diseases. Further, selective inhibitors of 17β-HSD1 could be used for prevention when there is a genetic disposition for breast cancer (Miettinen, M. et al., J. Mammary Gland. Biol. Neoplasia, 5: 259-270 (2000)).
Thus, this enzyme would suggest itself as a target for the development of novel selective and non-steroidal inhibitors as therapeutic agents in the battle against estrogen-related diseases. However, there has not been a proof of concept to date.
In the literature, only a few compounds have been described as inhibitors of 17β-HSD1 (Poirier, D., Curr. Med. Chem., 10: 453-477 (2003)). Most inhibitors are steroidal compounds obtained by different variations of the estrogen skeleton (Allan, G. M. et al., J. Med. Chem., 49: 1325-1345 (2006); Deluca, D. et al., Mol. Cell. Endocrinol., 248: 218-224 (2006); WO2006/003012; US2006/652461; WO2005/047303).

Another class of compounds which has been described is the so-called hybrid inhibitors (Qiu, W. et al., FASEB J., 16: 1829-1830 (2002); online: doi 10.1096/fj.02-0026fje), compounds that, due to their molecular structure, not only attack at the substrate binding site, but also undergo interactions with the cofactor binding site. The inhibitors have the following structure:                adenosine moiety or simplified derivatives that can interact with the cofactor binding site;        estradiol or estrone moiety, which interacts with the substrate binding site; and        a spacer of varying length as a linking element between the two moieties.        

Among these compounds, inhibitors have been synthesized that exhibit a good inhibition of the enzyme and a good selectivity for 17β-HSD2 (compound B (Lawrence, H. R. et al., J. Med. Chem., 48: 2759-2762 (2005))). In addition, the inventors consider that a small estrogenic effect can be achieved by a substitution at the C2 of the steroid skeleton (Cushman, M. et al., J. Med. Chem., 38: 2041-2049 (1995); Leese, M. P. et al., J. Med. Chem., 48: 5243-5256 (2005)); however, this effect has not yet been demonstrated in tests.
However, a drawback of these steroidal compounds may be a low selectivity. With steroids, there is a risk that the compounds will also attack other enzymes of the steroid biosynthesis, which would lead to side effects. In addition, due to their steroidal structure, they may have an affinity for steroid receptors and function as agonists or antagonists.
Among the phytoestrogens, which have affinity for the estrogen receptor and act as estrogens or anti-estrogens depending on the physiological conditions, flavones, isoflavones and lignans have been tested for an inhibitory activity (Makela, S. et al., Proc. Soc. Exp. Biol. Med., 217: 310-316 (1998); Makela, S. et al., Proc. Soc. Exp. Biol. Med., 208: 51-59 (1995); Brooks, J. D. et al., J. Steroid Biochem. Mol. Biol., 94: 461-467 (2005)). Coumestrol was found to be particularly potent, but of course showed estrogenic activity (Nogowski, L., J. Nutr. Biochem., 10: 664-669 (1999)). Gossypol derivatives were also synthesized as inhibitors (US2005/0228038). In this case, however, the cofactor binding site rather than the substrate binding site is chosen as the target site (Brown, W. M. et al., Chem. Biol. Interact., 143-144, 481-491 (2003)), which might entail problems in selectivity with respect to other enzymes utilizing NAD(H) or NADP(H).

In addition to diketones, such as 2,3-butanedione and glyoxal, which were used for studies on the enzyme, suicide inhibitors were also tested. However, these were found not to be therapeutically utilizable since the oxidation rate of the alcohols to the corresponding reactive form, namely the ketones, was too weak (Poirier, D., Curr. Med. Chem., 10: 453-477 (2003)).
In other studies, Jarabak et al. (Jarabak, J. et al., Biochemistry, 8: 2203-2212 (1969)) examined various non-steroidal inhibitors for their inhibitory effect, U-11-100A having been found as the most potent compound in this group. However, as compared to other non-steroidal compounds, U-11-100A is a weak inhibitor of 17β-HSD1.

As further non-steroidal inhibitors, thiophenepyrimidinones have been examined (US2005/038053; Messinger, J. et al., Mol. Cell. Endocrinol., 248: 192-198 (2006); WO2004/110459).
In addition, some phenylnaphthalene and phenylquinoline derivatives have been known from the literature:
6-(3-Hydroxyphenyl)naphthalene-2-ol, 6-(2-hydroxyphenyl)naphthalene-2-ol and 6-phenylnaphthalene-2-ol have been described as compounds having estrogenic activity (Cassebaum, H., Chemische Berichte, 90: 2876-2888 (1957); WO2005/014551; WO2003/051805; Mewshaw, R. E. et al., J. Med. Chem., 48: 3953-3979 (2005); Shunk, C. et al., J. Am. Chem. Soc., 71: 3946-3950 (1949); Tao, B. et al., Tetrahedron Letters, 43: 4955-4957 (2002); Hey, D. et al., J. Chem. Soc., 374-383 (1940).
4-(Naphthalene-2-yl)phenol has been described in WO2006/045096; Mewshaw, R. et al., J. Med. Chem. 48: 3953-3979 (2005), and WO2003/051805. Further derivatives of 4-(naphthalene-2-yl)phenol are known from WO2003/051805 and Smyth, M. S. et al., J. Med. Chem., 36: 3015-3020 (1993).
3-(Naphthalene-2-yl)phenol (Eichinger, K. et al., Synthesis, 8: 663-664 (1991); Nasipuri, D. et al., J. Chem. Soc. [Section] D: Chemical Communications, 13: 660-661 (1971); Raychaudhuri, S. R., Chem. Ind., 7: 293-294 (1980)), 4-(quinoline-3-yl)phenol (Cacchi, S. et al., Tetrahedron, 52: 10225-10240 (1996); Kaslow, C. et al., J. Org. Chem., 23: 271-276 (1958); Ma, Z. Z. et al., Phytochemistry, 53: 1075-1078 (2000)) and 2-(3-hydroxyphenyl)quinoline-6-ol (Kamenikova, L., Folia Pharmaceutica (Prague), 4: 37-71 (1982)) have been described as compounds having an analgetic effect.
4-Carboxy-2-(3-carboxy-4-hydroxyphenyl)quinoline, 4-carboxy-6-hydroxy-2-(3-hydroxyphenyl)quinoline, 2-(3-carboxyphenyl)quinoline, 4-carboxy-2-(3,4-dihydroxyphenyl)quinoline and 4-carboxy-7-hydroxy-2-(3,4-dihydroxyphenyl)-quinoline are known from U.S. Pat. No. 1,181,485, Bass, R. J., Chem. Ind., 17: 849 (1973), Gilman, H. and Soddy, T. S., J. Org. Chem., 23: 1584-85 (1958), and Holdsworth, M. G. and Lions, F., J. Proc. Royal Soc. NSW, 66: 473-476 (1933), respectively.
2-(3-Hydroxy-4-methoxyphenyl)quinoxaline, 2-(3-hydroxyphenyl)quinoxaline and 2-(3,4-dihydroxyphenyl)quinoxaline are known from Kovacs, Ö. et al. in Chem. Ber. 84: 795-801 (1951), and in Chem. et Phys., 3: 35-37 (1950).
3-(Quinoline-3-yl)phenol is a commercial product (Akos Consulting Solution GmbH, Basel, Switzerland, Order No. BH-1322; Aurora Fine Chemicals, Graz, Austria, Order No. kaccm-0002421).
WO2003/051805 further describes a wide variety of compounds having a 6-(4-hydroxyphenyl)naphthalene-2-ol skeleton that are estrogen receptor ligands with a high estrogen receptor affinity and a high estrogen receptor agonistic activity (estrogenicity). To date, however, none of the compounds mentioned has been reported as an inhibitor of 17β-HSD1. Since the compounds have been optimized for high estrogen receptor affinities, a strong inhibition of 17β is not to be expected in the first place. However, even if the compounds were inhibitors of 17β-HSD1, their strong estrogen receptor affinities would result in a systemic effect. However, such a systemic effect is just not desirable for certain applications.